There has been increasing demand in recent years for flexible, thinner, lightweight absorbent structures to resolve various problems of manufacturing, marketing, design, fit, wearing comfort, distribution, garbage disposal, material and energy consumption, transportation and storage costs and the like.
It is known from the art to introduce absorbent particulate polymer material into a matrix of cellulose fibers so as to create an absorbent structure whereby the absorbent particulate polymer material is capable of absorbing, distributing and retaining liquid while the cellulose fiber matrix acts as a grid, keeping absorbent particulate polymer material in its desired location. However, since the presence of cellulose fibers, usually wood pulp or fluff, results in relatively thick and bulky products, the process of manufacturing fluff involves cutting down trees and treating the wood pulp with various chemicals and transportation of the raw materials and end product is typically done over relative large distances, the product and process is considered to be less environmentally friendly. Hence there has been a desire to manufacture such absorbent structures without the use of wood pulp.
Many attempts have been undertaken to manufacture flexible, thin and lightweight absorbent structures, consisting of an absorbent material bonded to one or more carrier layers. However, the physical and/or chemical interaction in between the absorbent material and the bonding material and/or the carrier material often leads to a reduced absorption, distribution and/or retention performance despite functional and/or structural requirements.
It has been found that it is important to at least partially immobilise the absorbent material by compartmentalizing, restraining and/or bonding it to the absorbent structure in such a way that the absorbent structure is able to hold the absorbent material in either dry, partially or fully liquid loaded state. Failing to provide said sufficient structural integrity results in loss of functional performance such as absorbent structure coherence, absorption and/or retention performance and partial or overall failure.
Moreover, it is equally important not to excessively restrict the absorbent material from expanding and/or swelling during the liquid uptake, as this would also have a negative impact on the absorption and/or retention performance of the absorbent structure.
Many efforts have tried to compromise in between securely immobilizing absorbent material within the absorbent structure, while still sufficiently allowing the absorbent material to freely expand and swell during use, which in relation to absorbent articles within the personal hygiene industry for instance include:
U.S. Pat. No. 4,381,783 discloses an absorbent article with an absorbent structure comprising pockets of absorbent polymer material. These pockets are provided as to confine the movement of the absorbent polymer material, in particular when the absorbent article is partially or fully loaded with bodily exudates. These pockets form part of an absorbent storage layer and are typically provided from cellulose fibres. Hence, as to achieve good immobilization of the absorbent polymer material according to the teaching of this patent relatively high amounts of cellulose fibre material are required, thus increasing cost, bulkiness and rigidity of the absorbent article and severely reducing and hindering the expansion and/or swelling capacity of the absorbent polymer materials. The provision of such pockets may also hinder the free distribution of liquids to the more absorbent areas of the absorbent core, for example the areas of absorbent polymer materials.
WO95/17868 discloses an absorbent structure comprising two fibre layers and an intermediate layer. This intermediate layer comprises an absorbent polymer material in an amount exceeding 120 g/m2 and particles of a thermoplastic material. While this construction certainly provides good immobilisation of the absorbent polymer material in the dry state, it seems that only a lesser immobilisation can be achieved in the liquid loaded state. The thermoplastic material appears to stretch to a much lesser extent than the potential swelling of the absorbent polymer materials. Therefore, in particular when the absorbent structure is to be used in an absorbent article to absorb and retain high amounts of bodily exudates, for example a diaper or pants, the absorbent structure disclosed herein may not be fully satisfactory.
EP724418 discloses an absorbent article which includes absorbent polymer material located in discrete pockets. The absorbent article comprises a first and a second carrier layer and water-sensitive attaching means for securing together the carrier layers and to provide a plurality of pocket regions. The article comprises absorbent polymer material located within said pocket regions. The water-sensitive attachment means provides a wet strength which is less than the separating force imparted by a swelling of that absorbent polymer material when that absorbent polymer material is exposed to bodily exudates. The absorbent article is said to provide an absorbent structure which more securely locates and contains the absorbent polymer material in a selected way of pockets when the article is dry. However, due to the construction of the pockets, and specifically due to the selection of the water-sensitive attachment means, these pockets are not able to be controlled when the article is partially or fully loaded with liquids. Therefore, it is believed that this absorbent article does not provide a satisfactory immobilization of the absorbent material in partially or fully liquid loaded state leading to functional/structural failure.
EP1447066 describes an absorbent core for an absorbent article which provides an improved immobilization of absorbent polymer material when the article is fully or partially bodily exudates loaded. Specifically disclosed is an absorbent core useful in an absorbent article comprising a non-woven substrate layer, a layer of thermoplastic material in the form of a hot melt adhesive which bonds to the substrate layer to define cavities there between, and an absorbent material held in these cavities. However, in order to adequately secure the absorbent material, one needs to use a significant amount of thermoplastic material, which leads to higher costs and more product rigidity. Also, due to its internal cohesion, the layer of thermoplastic material exerts pressure and offers resistance against the free swelling of the absorbent material. Furthermore the high quantities of thermoplastic material may often lead to shielding and/or blocking of the absorbent polymer materials leading to reduced absorption and retention performance. Therefore, it is believed that this absorbent core does not provide satisfactory immobilization of absorbent materials in liquid loaded states. Additionally, the use of thermoplastic materials, glue or adhesives is considered to be less environmentally-friendly as they contain chemicals of a non-naturally renewable source and are based upon a complex chemical manufacturing process. Hence there has been a desire to manufacture such absorbent structures without the use of significant amounts of thermoplastic materials, glues, binders or adhesives.
Whilst the above attempts describe various approaches to the above identified problems, it is believed that none of these absorbent structures leads to very performing absorbent articles. The absorbent capacity left unused and the complex manufacturing processes makes neither of the above absorbent articles technically, economically and/or environmentally advantageous.
Also, many prior art absorbent structures have a relatively homogeneous distribution of absorbent material in the main acquisition layer and/or storage layer and therefore exhibit a substantially homogeneous swelling in said area. For second, third and next liquid insults, these absorbent layers may act as a liquid barrier due to the fact that these absorbent materials generally lose on liquid uptake and/or absorption capability once they are at least partially wetted and in a certain liquid expanded swollen states. This results in slowing down and slowed down liquid absorption and distribution, which eventually leads to extra leakage.
The problem mentioned above typically arises in absorbent articles, such as disposable baby diapers, where the absorbent substance is an absorbent polymer material, which is excessively and substantially homogeneously and continuously distributed over a narrow crotch width. Typical high levels of absorbent polymer material (especially levels in excess of about 15-35%) as used in absorbent cores tend to induce a phenomenon referred to as “gel-blocking”.
Gel-blocking occurs when the absorbent polymer material located in regions of first contact with fluid insults start to increase in volume as a consequence of imbibing the fluid, thereby forming a hydro-gel. When absorbent polymer material concentrations are high and wetted, the hydro-gel can block the initial and/or additional fluid from reaching other more absorbent regions of the absorbent core, thus leading to unappreciated, underused and/or unused absorbent capacity.
The occurrence of gel blocking and hydro-gelling can lead to too slow or limited liquid uptake, distribution and/or retention resulting in leakage during usage of the absorbent article. To remedy this problem, absorbent article designers have and typically use additional side cuffs, leakage barriers and/or acquisition and distribution layers which are expensive, inefficient and can only partly remedy these problems and limitations.
Hence, there is still an need in the art for an improved thin, flexible, lightweight absorbent structure for the use in an absorbent article which overcomes the problems of the prior art, which essentially comprises an absorbent structure with at least partially clustered, immobilized and/or restrained absorbent materials having effective and efficient fluid management during absorption, distribution and retention of bodily exudates. There is furthermore also a need for a method and apparatus to produce such absorbent structures at high production speed and low energy and raw material consumption.
Additionally, the present invention aims to provide improved absorbent structures, and elements for use therein, as well as absorbent articles utilizing such structures, utilizing integrated fluid management structures in and/or upon the absorbent core that effectively and efficiently absorbs the wearer's discharged body fluids upon initial and successive discharges, distributes and transports the absorbed liquid, from both initial and successive discharges over a relatively large proportion of the absorbent structure surface area, and allows for such discharged fluids to be effectively and efficiently stored.